Rechargeable batteries manufactured from laminates of solid polymer electrolytes and sheet-like anodes and cathodes display many advantages over conventional liquid electrolyte batteries. These advantages include lower overall battery weight, high power density, high specific energy, longer service life, as well as being environmentally friendly since the danger of spilling toxic liquid into the environment is eliminated.
Solid lithium polymer battery components include positive electrodes, negative electrodes and an insulating material capable of permitting ionic conductivity, such as a solid electrolyte consisting of a polymer and a lithium salt sandwiched between the positive and negative electrodes. The anodes or negative electrodes are usually made of light-weight metals foils, such as alkali metals and alloys, typically lithium metal, lithium oxide, lithium-aluminum alloys and the like. The composite cathodes or positive electrodes are usually formed of a mixture of active material such as transitional metal oxide, an electrically conductive filler, usually carbon particles, and an ionically conductive polymer electrolyte material, the mixture being set on a current collector, which is usually a thin sheet of aluminum. Since solid polymer electrolytes are less conductive than liquid polymer electrolytes, solid or dry electrochemical cells must be prepared from very thin films (total thickness of approximately 50 to 250 microns) to compensate the lower conductivity with high film contact surfaces and to provide electrochemical cells with high power density.
Composite cathode thin films are usually obtained by solvent coating onto a current collector or by melt extrusion. Similarly, the polymer electrolyte separator layer is typically produced by solvent coating or by melt extrusion.
Solid lithium polymer electrochemical cells are typically manufactured by separately preparing the positive electrode, the electrolyte separator and the negative electrode. The positive electrode is initially coated onto a metallic foil (for example aluminum) or onto a metallized plastic film, which serves as a current collector. The polymer electrolyte is coated onto a plastic substrate, such as a film of polypropylene. The positive electrode is thereafter laminated onto one face of the electrolyte, then the plastic substrate is removed from the second face of the electrolyte and the lithium negative electrode is applied thereon. This manufacturing process which is reasonably efficient for research and development and small scale production of lithium polymer electrochemical cells is inadequate for large scale production. U.S. Pat. No. 5,536,278 to Armand et al. disclosed one such method of assembling the various components of a solid lithium polymer electrochemical cells.
U.S. Pat. No. 5,100,746 to Gauthier disclosed a method of laminating simultaneously a plurality of layers of components of an electrochemical cell that is adapted to speed up the manufacturing process, wherein double-layer solid polymer electrolyte/composite positive electrode sub-assemblies are subsequently associated with the other constituent layers of the electrochemical cell. However, the double-layer solid polymer electrolyte/composite positive electrode sub-assemblies are previously produced by successive lamination of positive electrodes and solid polymer electrolytes.
In order to improve the efficiency of the production process for large scale manufacturing of lithium polymer batteries, there is a need for a faster yet reliable method and apparatus for the production of multiple-layer solid polymer electrolyte/composite positive electrode sub-assemblies for thin film solid lithium polymer electrochemical cells.